1. Field of the Invention
The present invention relates to a printer for positioning a platen provided on a cover frame with respect to a print head provided on a body frame when the cover frame is closed.
2. Related Art
In the related art, there is known a printer for storing a continuous paper such as a rolled paper therein and carrying out printing while pulling out the continuous paper. In a printer of this type, to change the continuous paper, it is necessary to manually pull out the continuous paper and take the continuous paper along a predetermined paper path. For this reason, a platen to be disposed in an opposite position to the print head is provided on the cover side of the printer for opening and closing a continuous paper exchange port such that the paper path is opened with an operation for opening a cover.
In the case in which the print head is of a dot impact type or an ink jet type, moreover, a predetermined gap (a platen gap) is to be maintained between the print head and the platen and the platen is to be provided in parallel with the printing line of the print head in order to assure printing quality.
However, the related art printer is positioned by the engagement of a lock lever provided rotatably on the cover frame and a lock pin provided on the body frame. Therefore, there is a possibility that positioning precision in the platen might be deteriorated by the influence of the attachment looseness of the cover frame to the body frame.
It is an object of the invention to provide a printer in which a platen provided on a cover frame can be positioned with high precision with respect to a print head provided on a body frame when the cover frame is closed. This high precision can be achieved by print head eliminating the influence of the attachment looseness of the cover frame to the body frame so that a predetermined gap can be maintained between the print head and the platen, and the platen can be provided in parallel with the printing line of the print head so that printing quality can be enhanced.
In order to attain the above object, the invention provides a printer comprising a print head provided on a body frame, a cover frame provided on the body frame to freely carry out an opening and closing operation, a platen provided on the cover frame and opposed to the print head with a predetermined gap when the cover frame is closed, a first positioning mechanism for positioning the platen with respect to the print head when the cover frame is closed to restrict a change in a position of the platen to a rotation around a first positioning fulcrum, and a second positioning mechanism for positioning the platen with respect to the print head when the cover frame is closed to restrict the rotation of the platen around the first positioning fulcrum by abutment on a second positioning fulcrum.
Moreover, it is preferable that the first positioning fulcrum should be provided on a first virtual line which passes through a printing position of the print head and is substantially perpendicular to a surface of the platen which is opposed to the print head with the predetermined gap when the cover frame is closed.
In short, a plane defined by the printing line and the first positioning fulcrum is substantially orthogonal to a surface of the platen which is opposed to the print head with the predetermined gap when the cover frame is closed.
In this case, the amount of a change in the platen gap caused by the rotation of the platen is minimized. Consequently, precision in the platen gap can be enhanced to improve printing quality.
Furthermore, it is preferable that the first positioning mechanism should include a lock pin provided on the body frame and acting as the first positioning fulcrum, a lock lever provided rotatably on the platen or the cover frame through a lock lever spindle and engaged with the lock pin to lock an operation for opening and closing the cover frame when the cover frame is closed, the lock lever is spindle provided on the platen or the cover frame and acting as the second positioning fulcrum, and a first positioning groove provided on the platen or the cover frame and serving to restrict a change in a position of the platen to only a rotation around the lock pin along an outer periphery of the lock pin when the cover frame is closed In this case, it is possible to constitute the first positioning mechanism by such a change as to add the first positioning groove to a related art lock lever mechanism. Therefore, the number of components can be reduced and the structure of the printer can be simplified.
Moreover, it is preferable that the second positioning mechanism should include a second positioning groove provided on the body frame and serving to restrict a rotation of the platen around the lock pin by abutment of the lock lever spindle on a groove inner edge portion when the cover frame is closed. In this case, the second positioning mechanism is constituted by utilizing a lock lever spindle. Consequently, the number of components can be reduced and the structure can be simplified. In addition, a distance between the first positioning fulcrum and the second positioning fulcrum is maintained to be constant by the lock lever. Consequently, positioning precision in the platen can further be enhanced.
Furthermore, it is preferable that the printer should further comprise a paper feed roller provided on one of the body frame and the cover frame, and a paper press roller provided on the other of the body frame and the cover frame and abutting on the paper feed roller when the cover frame is closed, the first positioning fulcrum being provided in a position offset from a second virtual line passing through centers of the paper feed roller and the paper press roller as seen from a side. In other words, the first positioning fulcrum is provided on an outside of a plane defined by an axis of the paper feed roller and that of the paper press roller.
In this case, a moment in a constant direction around the first positioning fulcrum is applied to the platen by a reaction force acting on the paper press roller. Therefore, the abutment position of the second positioning fulcrum and the second positioning groove can be specified to further enhance the positioning precision in the platen.
Moreover, it is preferable that the printer should comprise a spring for urging the paper press roller toward the paper feed roller side. In this case, a constant reaction force (spring force) acts on the paper press roller. Therefore, a moment in a constant direction can be reliably applied to the platen.